Quick Settings surface opacity

Quick settings is now translucent, inheriting the same color
but overriding its opacity.

Bug: 37013527
Test: visual - open qs and see transparency
Change-Id: I5a08758bcbdee33a316f669498592265809401a3

packages/SystemUI/res/color/qs_background_dark.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2017 The Android Open Source Project
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+
+<selector xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:alpha="0.93"
+          android:color="?android:attr/colorPrimaryDark"/>
+</selector>

packages/SystemUI/res/drawable/qs_background_primary.xml

@@ -15,6 +15,6 @@
 -->
 <inset xmlns:android="http://schemas.android.com/apk/res/android">
     <shape>
-        <solid android:color="?android:attr/colorPrimaryDark"/>
+        <solid android:color="@color/qs_background_dark"/>
     </shape>
 </inset>